Man that sucks. I remember an exciting ride when the hood on my dads 58 Metropolitan flew open on the freeway. It didn't damage the top either, but it smashed the windshield. And with hoods for these trucks being so hard to find, it's fortunate you found one even if it is $300.
I was at a local car show a few weeks ago and one of the participants offered me a 63 GMC hood for $100. It was "cherry", with nothing but a long scratch in the top. Unfortunately the long scratch turned out to be the center of the top caved in enough to hold about 2 quarts of water. Hopefully yours will turn out to be more cherry than what I saw.